Acrylic functional organosiloxane polymers (silicones) are well known. Such materials have found particular use as components of radiation-curable release coatings for which bulk cured properties have little importance.
In U.S. Pat. No. 3,886,865 there are described compositions useful for producing ink repellent areas on a printing plate which are solutions of certain methacrylate functional silicones. The silicones are essentially solid materials which may be produced by condensation of a hydroxy or chloro terminated dimethylsilicone with a hydrolyzate of phenyltrichlorosilane and methacryl functional silanes having three hydrolyzable groups. The trifunctional ingredients will produce highly cross-linked polymers of undefined structure which are nonflowable at room temperature.
In U.S. Pat. No. 4,387,240 there are described low molecular weight oligomers having a high methacrylate density which may be represented by the formula: ##STR3## where m is 1, 2 or 3; p is 2-10 and Q is methacryloxypropyl or similar groups. These oligomers are used as binders in dental filling compositions to give hard abrasion resistant cured fillings.
In U.S. Pat. No. 4,424,328 there are described branched low molecular weight siloxane compounds with 3 or 4 of the branches terminated with methacryloxypropyl groups. These compounds are used in the preparation of hard contact lenses.
In U.S. Pat. No. 4,035,355 there are described anaerobically cured acrylic functional silicone resins. These are randomly copolymerized materials which must have a minimum functionality, as defined in that reference, of 2.2 to cure. These resins have very high cross-link density which will result in rigid cured products.
In co-pending application Ser. No. 571,036, filed Jan. 16, 1984, there are described reinforced compositions of UV curable silicones having terminal acrylic groups and elongated acrylate-free intermediate regions which cure under UV irradiation to tough rubbers. The low acrylic functionality density of these resins, however, makes it difficult, if at all possible, to cure them with chemical free radical generators at ambient temperatures.
There therefore exists a need for silicone resins which can be cured to tough rubbery products by chemical free radical generators, particularly anaerobic cure systems. There also exists a need for UV curable acrylic silicone polymers of higher molecular weight or which may be cured to rubbery products at faster speed.
It is an object of this invention to produce an acrylic functional silicone polymer, curable to an elastomer, which has a liquid flowable consistency and which can be readily cured even by chemical free radical generators at ambient temperatures. The inventive polymers extend the range of molecular weight of acrylated silicone polymers which may be cured to tough rubbers by UV irradiation. These objects and others which will become apparent from the following discussion are met with novel "cluster" acrylic silicone resins of the present invention.